(1) Field of the Invention
This invention relates to methods for the preparation of platinum containing colloidal dispersions and methods for adsorbing such dispersions to a support material which may be used in an electrode for a fuel cell.
(2) Description of the Prior Art
Catalytic activity of a platinum catalyst will, as a general rule, increase with the increasing surface area of platinum. To achieve the increased surface area, it is necessary to prepare platinum catalyst in a finely divided form, that is, platinum catalyst having an average diameter below about 50 A.
It is known to prepare platinum catalysts in a number of ways: the most common methods are direct adsorption and precipitation. Chloroplatinic acid is one of the least expensive forms of platinum. Chloroplatinic acid does not adsorb directly on carbon black, a support material, in appreciable quantities.
Precipitation by slow reduction of chloroplatinic acid is a commonly employed approach. Bond, (Trans. Farady Soc., 52, 1235 (1956)) prepared 15 A particle size platinum using sodium citrate. Barber (U.S. Pat. No. 3,440,107), Arcano (U.S. Pat. No. 3,457,116), Turkevich et al (Science, 169, p. 873, 1970), and Bryce-Smith et al (German Pat. No. 2,117,439) used respectively silanes, alcohols, tartarates and napthalides, to produce high surface area platinum catalysts.
More recently, Petrow (U.S. Pat. Nos. 4,044,193; 3,992,512 and 3,992,331) obtained similar results using elaborate and complex recipes involving formation of a platinum sulfite complex acid as an intermediate followed by oxidation treatment to produce a substance containing platinum from chloroplatinic acid.
Although the above-mentioned literature discloses methods which are said to provide fine platinum particles, the methods require elaborate and complex steps or require relatively expensive reactants.
It is one object of the present invention to provide a method of making highly dispersed platinum having an average diameter below about 50 A, preferably below about 25 A. It is another object to provide highly dispersed platinum that is capable of being readily adsorbed on a support material.
It is another object of the present invention to provide a simplified method of obtaining the desired platinum particles and to use relatively inexpensive reactants.
It is another object of the present invention to provide a method of making a platinum catalyst adsorbed to support material made of carbon.